The present invention relates to a mechanism for reducing the number and degree of wrinkles within a web being printed on a printing press and, in particular, is directed to an anti-wrinkle roller construction for utilization with an offset continuous web newspaper press.
In continuous printing operations wherein a long sheet of paper is unrolled from a supply roll, especially newspaper printing, longitudinal wrinkles are a frequent problem. The wrinkles may be the result of one or more of the printing cylinders or guide rollers of the press being skewed so as to not rotate parallel to the axis of the paper supply or to other cylinders or rollers which over a period of time causes a difference in the tension on opposite sides of the paper web. Because of the difference in tension the paper tends to be urged transversely toward one side or the other of the web and longitudinally fold about some intermediate location. There are numerous other potential causes for a change in the tension of one side of the paper web from the other or of the sides relative to the center of the web, including poor paper stock in which the paper is inconsistent in thickness across the width of the web. As the paper supply rolls are usually quite large and the variance in thickness may be present along the entire length of the web, this small difference in paper thickness can accumulate over a substantial printing run with the result that the paper becomes taut or tensioned in certain locations across the width as it passes over the various rollers and cylinders of the press while being loose in other locations, thereby leading to the previously mentioned folds.
Sometimes the folds will not set or remain in the paper, but if the ink is applied while the fold is still there, then there will be a separation between the ink on opposite sides of the fold once the fold releases. On the other hand, if the fold sets after the ink has been placed on the web, then a portion of the printing will be precluded by the edges of the fold. Folds are often more likely to set or stay in the web in processes where the web is slightly dampened, for example, in offset printing where a dampening fluid is utilized.
Attempts have been previously made to provide a guide cylinder that would have an axis that could be skewed relative to other cylinders and rollers within a printing press to especially accommodate misalignment of the press rollers with the paper supply roll axis. Unfortunately, these cylinders are approximately the same width as the other cylinders within the press; it is only possible to make gross adjustment of the tension between the opposite sides of the web; and positioning such a cylinder to apply increased tension to one side of the web inherently prevents applying increased tension to the opposite side. What is desirable is a mechanism which will allow independent tensioning or relaxation of the web on either side thereof both relative to each side and to the center of the web. In this manner adjustment and tension can be made where, for example, the center of the paper is slightly thinner than either side.
It is noted that the theory associated with using a cylinder to adjust the tension on the web is basically as follows. If the web passes over the cylinder in such a manner that a transverse cross-section of the web in the longitudinal center of the part of the web engaging the cylinder is always parallel to the axis of the cylinder, then no relative relaxation or tension will be placed upon the web by that particular cylinder. On the other hand, if a first end of the cylinder is relatively radially outward in the direction of the web from the overall axis of rotation of the cylinder, while the cylinder opposite end is slightly radially inward toward the axis of rotation of the cylinder relative to the first end, then the edge of the web that engages the first end will have to travel further than the edge of the web that engages the second end. In such a configuration, as the web passes over the roller during a long printing run, relative tensioning begins to occur in the first end of the web and relative relaxing occurs in the second end of the web relative to the center of the web. This tensioning and relaxation on opposite sides of the web can be utilized to counterbalance opposite tensioning and relaxation produced in the web at the other locations or occurring naturally.